First of all, Don't assume too much about Devin too quickly.
The difference between Mickey and Mikey is basically a preference of the individual and/or his parents. Both are acceptable nicknames for Michael.
As far as Mc and Mac, Mc is the start of Irish surnames, such as McCarthy, McCann. and McNally. as well as Scottish surnames, such as McDonald, McKeller, and McPhee.
Mac is the start of Irish surnames such as MacCormack, MacDermot, and MacNamara, as well as Scottish surnames such as MacAllister, MacGregor and MacNeil.
Therefore, you can see that Mc and Mac are used in both Celtic and Gaelic names, so you can't make generalities about a person's origin by merely categorizing the Mc as Irish and Mac as Scottish. You have to look at and compare the surnames to determine their origin. I hope this helps.